AuroraMiddleware/glibc
1
0
Fork 0
mirror of https://sourceware.org/git/glibc.git synced 2024-12-22 10:50:07 +00:00
Code Issues Packages Projects Releases Wiki Activity

Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT

Browse Source 
According to Silvermont software optimization guide, for 64-bit
applications, branch prediction performance can be negatively impacted
when the target of a branch is more than 4GB away from the branch.  Add
the Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable
pages with MAP_32BIT first.  NB: MAP_32BIT will map to lower 2GB, not
lower 4GB, address.  Prefer_MAP_32BIT_EXEC reduces bits available for
address space layout randomization (ASLR), which is always disabled for
SUID programs and can only be enabled by setting environment variable,
LD_PREFER_MAP_32BIT_EXEC.

On Fedora 23, this patch speeds up GCC 5 testsuite by 3% on Silvermont.

	[BZ #19367]
	* sysdeps/unix/sysv/linux/wordsize-64/mmap.c: New file.
	* sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/mmap.c: Likewise.
	* sysdeps/x86/cpu-features.h (bit_Prefer_MAP_32BIT_EXEC): New.
	(index_Prefer_MAP_32BIT_EXEC): Likewise.
This commit is contained in:
H.J. Lu 2015-10-21 14:44:23 -07:00
parent c9afcaaafa
commit b9eb92ab05
4 changed files with 124 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
sysdeps/unix/sysv/linux/wordsize-64/mmap.c Normal file
View File

@ -0,0 +1,40 @@
/* Linux mmap system call. 64-bit version.
Copyright (C) 2015 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <sys/types.h>
#include <sys/mman.h>
#include <errno.h>
#include <sysdep.h>
/* An architecture may override this. */
#ifndef MMAP_PREPARE
# define MMAP_PREPARE(addr, len, prot, flags, fd, offset)
#endif
__ptr_t
__mmap (__ptr_t addr, size_t len, int prot, int flags, int fd, off_t offset)
{
MMAP_PREPARE (addr, len, prot, flags, fd, offset);
return (__ptr_t) INLINE_SYSCALL (mmap, 6, addr, len, prot, flags,
fd, offset);
}
weak_alias (__mmap, mmap)
weak_alias (__mmap, mmap64)
weak_alias (__mmap, __mmap64)

44
sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h Normal file
View File

@ -0,0 +1,44 @@
/* Optional code to distinguish library flavours. x86-64 version.
Copyright (C) 2015 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#ifndef _DL_LIBRECON_H
#include <sysdeps/unix/sysv/linux/dl-librecon.h>
/* Recognizing extra environment variables. For 64-bit applications,
branch prediction performance may be negatively impacted when the
target of a branch is more than 4GB away from the branch. Add the
Prefer_MAP_32BIT_EXEC bit so that mmap will try to map executable
pages with MAP_32BIT first. NB: MAP_32BIT will map to lower 2GB,
not lower 4GB, address. Prefer_MAP_32BIT_EXEC reduces bits available
for address space layout randomization (ASLR). Prefer_MAP_32BIT_EXEC
is always disabled for SUID programs and can be enabled by setting
environment variable, LD_PREFER_MAP_32BIT_EXEC. */
#define EXTRA_LD_ENVVARS \
case 21: \
if (memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \
GLRO(dl_x86_cpu_features).feature[index_Prefer_MAP_32BIT_EXEC] \
= bit_Prefer_MAP_32BIT_EXEC; \
break;
/* Extra unsecure variables. The names are all stuffed in a single
string which means they have to be terminated with a '\0' explicitly. */
#define EXTRA_UNSECURE_ENVVARS \
"LD_PREFER_MAP_32BIT_EXEC\0"
#endif /* dl-librecon.h */

37
sysdeps/unix/sysv/linux/x86_64/64/mmap.c Normal file
View File

@ -0,0 +1,37 @@
/* Linux mmap system call. x86-64 version.
Copyright (C) 2015 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <ldsodefs.h>
/* If the Prefer_MAP_32BIT_EXEC bit is set, try to map executable pages
with MAP_32BIT first. */
#define MMAP_PREPARE(addr, len, prot, flags, fd, offset) \
if ((addr) == NULL \
&& ((prot) & PROT_EXEC) != 0 \
&& HAS_ARCH_FEATURE (Prefer_MAP_32BIT_EXEC)) \
{ \
__ptr_t ret = (__ptr_t) INLINE_SYSCALL (mmap, 6, (addr), (len), \
(prot), \
(flags) | MAP_32BIT, \
(fd), (offset)); \
if (ret != MAP_FAILED) \
return ret; \
}
#include <sysdeps/unix/sysv/linux/wordsize-64/mmap.c>

3
sysdeps/x86/cpu-features.h
View File

@ -33,6 +33,7 @@
#define bit_AVX512DQ_Usable (1 << 13) #define bit_AVX512DQ_Usable (1 << 13)
#define bit_I586 (1 << 14) #define bit_I586 (1 << 14)
#define bit_I686 (1 << 15) #define bit_I686 (1 << 15)
#define bit_Prefer_MAP_32BIT_EXEC (1 << 16)
/* CPUID Feature flags. */ /* CPUID Feature flags. */
@ -97,6 +98,7 @@
# define index_AVX512DQ_Usable FEATURE_INDEX_1*FEATURE_SIZE # define index_AVX512DQ_Usable FEATURE_INDEX_1*FEATURE_SIZE
# define index_I586 FEATURE_INDEX_1*FEATURE_SIZE # define index_I586 FEATURE_INDEX_1*FEATURE_SIZE
# define index_I686 FEATURE_INDEX_1*FEATURE_SIZE # define index_I686 FEATURE_INDEX_1*FEATURE_SIZE
# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1*FEATURE_SIZE
# if defined (_LIBC) && !IS_IN (nonlib) # if defined (_LIBC) && !IS_IN (nonlib)
# ifdef __x86_64__ # ifdef __x86_64__
@ -248,6 +250,7 @@ extern const struct cpu_features *__get_cpu_features (void)
# define index_AVX512DQ_Usable FEATURE_INDEX_1 # define index_AVX512DQ_Usable FEATURE_INDEX_1
# define index_I586 FEATURE_INDEX_1 # define index_I586 FEATURE_INDEX_1
# define index_I686 FEATURE_INDEX_1 # define index_I686 FEATURE_INDEX_1
# define index_Prefer_MAP_32BIT_EXEC FEATURE_INDEX_1
#endif /* !__ASSEMBLER__ */ #endif /* !__ASSEMBLER__ */